Roadmap: Profiling and Debugging
This roadmap will introduce profiling and debugging, two techniques for performing analysis of the runtime behavior of an application. Effective use of profiling and debugging techniques requires a basic understanding of system-level details related to compiling, linking, storing, and running executables, which this roadmap will discuss.
Profiling and debugging have different goals. Profiling focuses on characterizing the performance of an application, while debugging focuses on diagnosing faults. In particular, Debugging:
- Helps one find defects, analyze failures, and analyze expected program flow.
- Inspects and modifies the state of a running program, or performs post-mortem analysis of failures via inspecting memory dumps.
- Is harder in parallel applications.
...while Profiling:
- Measures performance characteristics, helping to identify areas for performance improvement.
- Collects performance measurements of a running program, analyzes results afterward.
- Is harder in parallel applications.
Profiling and debugging tools and techniques for parallel applications will be discussed along with a survey of profiling and debugging tools available on Frontera at TACC.
Objectives
After you complete this roadmap, you should be able to:
- Apply ad-hoc ("printf") and symbolic debugging techniques at runtime
- Perform basic debugging steps with
gdb - Describe the advantages of using a debugging tool such as DDT (for parallel codes)
- Enhance code performance through detailed performance profiling
- Distinguish between instrumentation and statistical sampling
- Demonstrate function-level profiling with
gprof - Identify the kinds of events tracked by PAPI
- Demonstrate profiling an MPI application with TAU
- Explain the difference between profiling and tracing
Prerequisites
This roadmap presumes a basic knowledge of Linux/Unix. Although specific programming knowledge is not required, it will provide significantly enhanced context and understanding. Most of the tools presented apply equally well to C, C++, and Fortran. The roadmap is not constructed with any of these languages specifically in mind.
Requirements
Most of the content in this roadmap is applicable to any Linux- or Unix-based system where GNU software is installed. Specific instructions are given for TACC systems, especially Frontera; however, these instructions can easily be tailored to different systems as well.